1. Field of the Invention
The present invention relates to a master carrier for magnetic transfer that carries information that is transferred magnetically to a slave medium.
2. Description of the Related Art
With an increase in information quantity, there is demand for a magnetic recording medium that has high memory capacity, is low in cost and capable of high-speed access to a desired block of data. As an example of such a magnetic recording medium, there is known a high recording density magnetic medium (magnetic disk medium) that is employed in a hard disk drive or flexible disk drive. To realize the high memory capacity, servo tracking technology has played an important role. In the servo tracking technology, the narrow data tracks are scanned accurately with a magnetic head to generate signals at a high signal-to-noise ratio (S/N ratio). To perform the servo tracking, a servo tracking signal, an address information signal, a clock signal, etc., are preformatted in the disk at predetermined intervals.
As a method for performing the pre-formatting accurately and efficiently, a magnetic transfer method of magnetically transferring information (such as a servo signal, etc.) carried by a master carrier to a magnetic recording medium has been disclosed, for example, in Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544, and 10(1998) -269566.
In the above magnetic transfer method, the master carrier has a pattern of protrusions provided with a magnetic layer on the surfaces thereof corresponding to information that is transferred to a magnetic recording medium (slave medium) such as a magnetic disk medium, and is brought into close contact with the slave medium. In this state, a magnetic field for magnetic transfer (hereinafter referred to as a transfer field) is applied so that a magnetization pattern corresponding to the information (for example, a servo signal) carried by the master carrier is transferred to the slave medium. Because magnetic recording can be performed statically without changing the relative position between the master carrier and the slave medium, accurate pre-formatting can be performed and the time required for pre-formatting is extremely short.
The master carrier that is used for magnetic transfer has a land/groove pattern, which is formed from a magnetic material by performing processes, such as photolithography, sputtering, etching, etc., on a silicon substrate, a glass substrate, or the like.
It is also possible to generate the aforementioned master carrier by utilizing lithography, which is used for integrated circuit (IC) fabrication, or a stamper technique, which is for optical disk stamper generation.
To enhance the quality of transfer in the aforementioned magnetic transfer, it is extremely important to bring the master carrier and the slave medium into close contact with each other without any gap. If the contact between the two is deficient, then regions where magnetic transfer is not performed will occur. If magnetic transfer is not performed, signal dropouts occur in the magnetic information transferred to the slave medium and therefore the signal quality is reduced. In the case where a signal recorded is a servo signal, the tracking function cannot be sufficiently obtained, and consequently, there is a problem that the reliability will be reduced.
In the aforementioned magnetic transfer, one or two flat master carriers are brought into close contact with one or both sides of a slave medium. Because of this, dust particles must not exist at the contact portion between the master carrier and the slave medium. If dust particles are present on the contact portion, stable magnetic transfer cannot be performed and there is a possibility that the master carrier or slave medium itself will be damaged.
In the magnetic transfer, relatively high pressure is applied on the master carrier and the slave medium to perform entire-surface contact. Because of this, if magnetic transfer is repeated a large number of times, and the number of contacts is increased, the magnetic layer formed on the substrate of the master carrier will be chipped in the magnetic transfer step. If the fragments of the chipped magnetic layer are present on the contact portion between the master carrier and the slave medium, they can reduce the quantity of transferred signals and can be the cause of deterioration in the durability of the master carrier.
The cause of the separation, etc., of the magnetic layer of the master carrier lies in a high chemical affinity between the magnetic layer of the master carrier and the magnetic layer, protective layer, and lubricant layer of the slave medium, the fragility of the magnetic layer itself with respect to external force, and so on. That is, when the master carrier and the slave medium are separated after magnetic transfer is performed with the master carrier held in close contact with the slave medium, force acts on the magnetic layer of the master carrier in a direction opposite to the substrate of the master carrier. Because of the high chemical affinity between the magnetic layer of the master carrier and the lubricant layer, protective layer, and magnetic layer of the/slave medium, if the force in the opposite direction is repeatedly applied on the magnetic layer, the separation of the magnetic layer from the master carrier occurs. In addition, in repeated use, the master carrier undergoes external force such as shock, etc., and therefore part of the magnetic layer is sometimes separated or chipped.
As a method for reducing the separation, etc., of the magnetic layer of the master carrier, a method of forming a diamond-like carbon (DLC) film on the magnetic layer surface of the master carrier, or a method of further forming a lubricant layer on the uppermost layer of the master carrier which makes contact with the slave medium, is disclosed in Japanese Unexamined Patent Publication No. 2000-195048 or 2001-14665. By forming the DLC film or lubricant layer, the separation, etc., of the magnetic layer of the master carrier are reduced to some degree and the durability of the master carrier is enhanced. However, these methods cannot prevent the separation, etc., of the magnetic layer completely. In addition, in the conventional magnetic layer, the size of the fragments of a separated or chipped magnetic layer, caused by separation, etc., often becomes great. Therefore, if separation occurs, poor magnetic transfer is caused by the separated or chipped magnetic layer and therefore transfer performance is deteriorated.
In the case where the separation, etc., of the magnetic layer occurs over a wide range, the number of signal dropouts exceeds an allowable range, and consequently, the use of the master carrier cannot be continued. As the master carrier is expensive, the number of slave media to which magnetic transfer is performed by a single master carrier is extremely important in reducing the manufacturing cost.
On the other hand, even in the case where the separation, etc., of the magnetic layer occurs, if the separated or chipped fragments are small, the influences such as transfer signal dropout and deficient close contact property which lead to poor magnetic transfer is slight. In this case, there is no reduction in the quantity of magnetic transfer and the use of the master carrier can be continued.